1. Field of the Invention
Apparatuses consistent with the present invention relate to moving a magnetic domain wall using a magnetic field application unit, and more particularly, to moving a magnetic domain wall by supplying current and applying a magnetic field at the same time in order to facilitate the motion of a magnetic domain wall in a magnetic layer.
2. Description of the Related Art
The unit of a magnetic region constituting a magnetic body is typically referred to as a magnetic domain. The directions of magnetic moments due to spins of electrons are the same in a single magnetic domain. The size and magnetic polarization of the magnetic domain may be appropriately controlled by the shape and size of a magnetic material and external energy applied thereto.
A magnetic domain wall is a boundary region between two magnetic domains. The magnetic domain wall can be moved by an externally applied magnetic field or current. A plurality of magnetic domains having specific magnetization directions may be generated in a magnetic layer with a predetermined width and thickness. Also, the magnetic domains and the magnetic domain wall therebetween may be moved by a magnetic field having an appropriate intensity or current.
The principle of magnetic domain wall motion may be applied to a data memory device. For example, when magnetic domains are allowed to pass through a predetermined read/write head using the principle of magnetic domain wall motion, the data memory device is capable of reading/writing data without rotating a recording medium. Since a data memory device using magnetic domain wall motion is structurally simple and has a small size, it is expected that the data memory device using magnetic domain wall motion can have a high recording density of 1 Tbit/in2 or higher.
However, the data memory device using magnetic domain wall motion is still in an initial developmental stage, and several problems need to be solved to put the data memory device using magnetic domain wall motion to practical use. For example, a high current density required for moving a magnetic domain wall is problematic. Thus, power consumption may increase and the motion of the magnetic domain wall may be impeded. The foregoing related art data memory device using magnetic domain wall motion has following problems.
First, when the related art data memory device using magnetic domain wall motion uses only current, a large current is required because data is written or read by pushing or pulling the magnetic domain wall. In comparison, when the related art data memory device using magnetic domain wall motion uses only a magnetic field, the data memory device needs a very complicated structure, so that increasing data density becomes difficult.
Second, when the critical current density required for moving a magnetic domain is high, a driver circuit of a memory chip should drive a large amount of current so that the data memory device needs a large area. Because the data memory device is characteristic of moving the magnetic domain at high speed, the supply of current should be allowed or cut off at a high frequency. In this case, however, the driver circuit of the memory chip should include a large driver transistor and the memory chip should consume more power to increase the supply of current at high speed. As a result, the reliability of the driver circuit may deteriorate.
Third, even if the foregoing configuration of the driver circuit is enabled, when a large current is supplied to the memory device, a large amount of Joule's heat is emitted, which raises the temperature of a memory cell so that the memory cell may perform unstable operations unlike at low temperatures. In other words, the memory device may lose written data due to its poor thermal stability.
Fourth, when the related art memory device uses only a magnetic field, the memory device is readily capable of moving one bit of data. However, when the memory devices moves several bits of data at the same time, a magnetization having the same direction as the magnetic field increases, while a magnetization having an opposite direction to the magnetic field decreases, so that the memory device may lose data. Therefore, it is difficult to perform precise operations, and the efficiency of the memory device is degraded when a magnetic field is applied to the memory device in a direction vertical to the magnetized polarization of the magnetic domain.
Fifth, when a magnetic field is applied to all memory cells, all the memory cells operate at the same time. Therefore, each of the memory cells should include a magnetic field application structure in order to make only a desired cell perform an operation. Accordingly, the entire structure becomes complicated to drive the respective memory cells. Thus, the related art memory device using magnetic domain wall motion cannot have high density like in a conventional magnetic random access memory (MRAM).